AD-LRU: An efficient buffer replacement algorithm for flash-based databases

Flash memory has characteristics of out-of-place update and asymmetric I/O latencies for read, write, and erase operations. Thus, the buffering policy for flash-based databases has to consider those properties to improve the overall performance. This article introduces a new approach to buffer management for flash-based databases, called AD-LRU (Adaptive Double LRU), which focuses on improving the overall runtime efficiency by reducing the number of write/erase operations and by retaining a high buffer hit ratio. We conduct trace-driven experiments both in a simulation environment and in a real DBMS, using a real OLTP trace and four kinds of synthetic traces: random, read-most, write-most, and Zipf. We make detailed comparisons between our algorithm and the best-known competitor methods. The experimental results show that AD-LRU is superior to its competitors in most cases.